This isn't a glitch, the tank line-ups actually list some tier V Lights (VK2801, Chaffee, T-50-2) above about half of the tier VI tanks. I'm not entirely sure why though, it probably has to do with the fact that they're the end of a tank line.

They aren't really tier V's per se. Most of them have modules far about their tier, they just haven't been able to translate them into their own tier much like they have with the French and American lines.

It's a bit odd though, because the Type 62 (which I'd say is about even with them in stats) was placed at tier 6. Ideally, WG would move the Chaffee, VK2801 and T50-2 to tier 6, and fill the gap in each line with a real tier 5.